1. Field of the Invention
The present invention relates to an image blur prevention apparatus that prevents the occurrence of blurred images when a camera or other optical devices are used.
2. Related Background Art
The conventional structure of an image blur prevention apparatus that is used for a camera, etc., is shown in FIG. 12. In accordance with the state of a switch 52, through a lock driving means 61, a control circuit 51, for controlling the entire apparatus, operates a lock mechanism 62 that mechanically locks and, in order to begin an image blur prevention operation, releases the lock of a correction system 59.
At the same time as this operation is being performed, the output, transmitted through a high pass filter 55 and an integral means 56, of a fluctuation sensor 54, which detects the movement of the hands of an individual, such as a photographer, who operates an optical device; the output of a correction system position detection means 60, which detects the positional shifting of a correction system 59; and the output of a driving center setting means 50, which sets a driving center by employing data it receives from an adjusted data setting means 63, are added together by an addition means 57 and the result is input to a correction system driving means 58. Then, the output of the correction system driving means 58 is employed to drive the correction system 59, which is provided in one part, or in front, of an exposure system.
Therefore, under the previously described feedback control for the correction system, as long as the phase of movement and the sensitivity of the correction system are set (i.e., an output at a unit correction angle), the positioning of the correction system, which is determined by the output of the fluctuation sensor 54 and the output of the driving center setting means 50, can be instantaneously adjusted, so that the blurring of an image, which can accompany the movement of the hands of an operator, can be expeditiously avoided.
In the prior art, however, the locking mechanism for the correction system is so designed that for a projection that is formed on the locking mechanism, which during the locking process, rapidly engages a recessed portion of the correction system, normally there is a certain amount of play provided by sizing errors that occur during manufacture and because of improvements made to increase the reliability of the locking operation. Therefore, when the control of the correction system 59 is in the OFF state and the correction system 59 is locked, the correction system 59 can be freely shifted within a range of movement that is provided by the play.
FIG. 13 specifically shows the range of movement afforded by the play in the mechanical locking when the correction system 59 is locked. As is shown in FIG. 13, the range of movement for the correction system 59, while it is in the locked state, defines a circle. In order for mechanical/optical positioning to be performed, the correction system is usually so designed that the center of the light axis is at the center of the play in the mechanical locking. A driving center, with which correction is to be performed based on the above-described sensor output, is also intended to correspond with the center of the play in the mechanical locking.
However, the position of the driving center of the correction system 59 differs, depending on the lenses employed, in accordance with the accuracy of the attachment of the correction system position detection means 60 and the offset for circuitry. The data for the individual lenses that are set by the adjusting data setting means 63 are used to provide corrections for correctly positioning the driving center so that its position corresponds with the center of the range of play for the mechanical locking. As was first described, when there is too little available play for the mechanical locking (e.g., the surface area of a recessed portion that is formed in the correction system is reduced), accordingly, the projection that is formed on the locking mechanism may not engage the recessed portion and it may not be possible to lock the correction system. Therefore, a certain amount of play must be provided to insure reliable locking.
If there is too much play in the locked portion, however, when the correction system, which gravity places in the outermost edge of the play before the initial locking is released, is moved to the center of the range of movement of the play at the same time as the locking is released, an image that has passed through the exposure system (to include the correction system) is greatly changed instantaneously, and an operator has a strong sense of incongruity when observing an object through a TTL view finder such as is used in a single-lens reflex camera.